Soil reservoir is the basis of stable grain production and sustainable development in dry farming area. Based on the long-term field experiment, we investigated the changes of soil moisture in wheat field located in the rain-fed Changwu Tableland, and analyzed the interannual and annual variation characteristics and dynamics trends of soil reservoir from 2012 to 2015. The results showed that the vertical distribution curves of average soil water content were "double peaks and double valleys": first peak and valley occurred in the 10-20 and 50 cm soil layer, respectively, while for the second peak and valley, the corresponding soil layer was the 100 and 280 cm soil layer. Soil reservoir did not coincide with precipitation for all yearly precipitations patterns but lagged behind. Yearly precipitation patterns had a great influence on the interannual and annual dynamic changes of soil reservoir. Compared with rainy year, the depth of soil moisture consumption decreased and supplementary effect of Precipitation on soil moisture became obviously under effects of drought year and normal year. In rainy year, soil reservoir had a large surplus (84.2 mm); in normal year, it had a slight surplus (9.5 mm); while in drought year, it was slightly deficient (1.5 mm). We can infer that in rainy year and normal year water balance was compensated, while in drought year water balance was negatively compensated. The dynamics of soil water in winter wheat field in the rain-fed Changwu Tableland can be divided into four periods: seedling period, slow consumption period, large consumption period, and harvest period and the order of evapotranspiration were large consumption period> seedling period> harvest period> slow consumption period.